The author ignores the possibility that environmental factors might cause or worsen the physical conditions that then result in psychoses. She assumes that psychoses “have nothing to do with environmental factors” and are caused only by physical factors.

The author doesn't ignore this possibility. She argues that psychoses, which she claims are caused by purely organic factors, are best treated with medicine.

The author doesn’t discuss this, but it doesn’t weaken her argument because she’s only addressing psychological illnesses. The treatment of nonpsychological illnesses is irrelevant.

The author actually seems to assume that the nature of a medical condition can be inferred from the nature of its treatment. She draws a conclusion about the nature of psychoses based on the nature of their treatment. So, (D) doesn’t describe something that the other ignores.

The author’s conclusion is about psychoses, not neuroses. She ignores the possibility that environmental factors may be at least partially responsible for psychoses.